The use of emulsions is widespread in cosmetics. An emulsion comprises a finely dispersed mixture of two liquids, such as fat bodies (oils, fatty alcohols, hydrocarbons or also fatty acid triglycerides) and water. One theory regarding emulsions is that one of the liquids (phase) forms small droplets which are present dispersed in the other liquid (phase). The phase that forms the droplets is referred to as the inner phase or also disperse phase. The phase in which the droplets float is called the outer phase or also the continuous phase.
In the case of emulsions that comprise a water phase and an oil phase, a distinction is made between oil-in-water emulsions (O/W emulsions) and water-in-oil emulsions (W/O emulsions). Classic O/W emulsions are described in the literature often as oil droplets which are dispersed in the continuous water phase and are stabilised at the interface of both phases by surfactants or emulsifiers. The latter form a film around the oil droplets and are thus able to reduce the surface tension. In complex cosmetic formulations, however, a number of various ingredients are generally used, thus resulting in complex multiphase systems.
In the field of hair dye agents and hair bleaching agents, the use of formulations that are based on high amounts of fatty alcohols (fatty amphiphiles) and surfactants is known. Lamellar networks, which are also described as lamellar gel networks or multilamellar structures, are often created in formulations of this type.
WO 2015/112787 A1 describes hair dyes that comprise a multilamellar emulsion and that, in addition to colouring substances, also contain a combination of polar nonionic surfactants and nonionic surfactants that are less polar.
EP 1 433 475 A1 relates to hair dye agents which, besides ammonia and oxidation dyes, also contain at least about 10% by weight of a mesomorphic phase, wherein the term “mesomorphic phases” also includes lamellar phases.
EP 1 761 235 B1 lastly claims dye agents which contain the oxidation dye precursors encapsulated in or adsorbed on multilamellar vesicles.
The dye agents described in these documents, however, cannot yet be considered optimal in respect of their application properties, in particular in respect of their stability.
In order to produce permanent, intense colourations with corresponding fastness properties, what are known as oxidation dyes are used. Such dyes usually contain oxidation dye precursors, or what are known as developer components and coupler components. The developer components form the actual colouring agent under the influence of oxidants or atmospheric oxygen, either on their own or with coupling to one or more coupler components. The oxidation dyes are exemplified by intense, outstanding, long-lasting colour results. A mixture of a greater number of oxidation dye precursors can be used for naturally acting colouring agents, wherein substantive dyes are also used additionally in many cases to provide further colour shades.
Oxidation dye precursors of the developer type are based typically on the basic structure of p-phenylenediamine, p-aminophenol, or heterocyclic di- or polyamino compounds. Substances of this type are extremely sensitive to atmospheric oxygen and are usually used in the form of their physiologically acceptable salts for stabilisation, i.e. the amino groups provided in the substances are converted—wholly or partially—into the amino groups present in the substances and are neutralised by counterions (chlorides, bromides, hydrogen sulfates or also sulfates). If a user wishes to colour their hair in a particularly dark hue, for example a dark brown or black shade, said user will thus use a corresponding dye agent with a particularly high colourant content. Due to the high content of oxidation dye precursors, the corresponding salt content in these agents is also very high.
Emulsions, such as O/W emulsions, often react very sensitively to an increase of their salt content. The risk that an emulsion or a dye agent will separate and prove unstable under storage is therefore particularly high in the case of shades having a high colourant content.